Pressure contact switch

ABSTRACT

A pressure contact switch for monitoring the inflation pressure of tires comprises a piston subjected on one side to the pressure of the air in the tire and on the other side to the force of an opposing calibrated spring. A rod coaxial with the piston is formed with an inclined cam surface to push back a contact slide capable of sliding in a first bore. The rod is also formed with a guide and stop for a locking slide capable of sliding in a second bore having an axis perpendicular to that of the first bore. The two slides are urged at all times by springs in directions towards the intersection of the two bores.

United States Patent [72] Inventor Daniel Lejeune [56] References Cited Clarmont-Ferrand, France UNlTED STATES PATENTS [21] A ppl. N 56,360 2,296,411 9/1942 Wills ZOO/61.25 Fllied y 20, 7 3,536,874 /1970 Van Ophem 200/82 D [45] Patented Oct. 5, 1971 [73] Assignee Compagnie Generale Des Etablissements prlrf'ary Micheline, raison sociale Michelin & Cie Amman Examme" M- Gmsburg Clerm0m Fe"and Puydemome France Attorney-Brumbaugh, Graves, Donohue & Raymond [32] Priority July 21, 1969 [33] France 6924849 ABSTRACT: A pressure contact switch for monitoring the inflation pressure of tires comprises a piston subjected on one side to the pressure of the air in the tire and on the other side [54] Z%? N SWITCH to the force of an opposing calibrated spring. A rod coaxial rawmg with the piston is formed with an inclined cam surface to push [52] US. Cl 200/61.25, back a contact slide capable of sliding in a first bore. The rod 200/ 83 J, 340/58 is also formed with a guide and stop for a locking slide capable [51] Int. Cl 1101b /24 of sliding in a second bore having an axis perpendicular to that [501' Field of Search ZOO/61.25, of the first bore. The two slides are urged at all times by 82 D, 83 J 340/58 springs in directions towards the intersection of the two bores.

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. l I 1 -24 y- Y l I I J/ 5 /3 4 2 72 E 3 I l I PRESSURE CONTACT SWITCH BACKGROUND OF THE INVENTION This invention relates to pressure contact switches: i.e., devices that monitor the pressure of a fluid in a sealed enclosure and effect the closing and/or opening of an electrical circuit when the pressure drops below and/or rises above predetermined values. It relates more particularly to novel and highly effective pressure contact switches intended to monitor the inflation pressure of tires.

In various patents there can be found a description of a large number of puncture alarm devices and pressure contact switches. Prior to the present invention, however, there has been no one truly satisfactory solution fulfilling all the conditions that should be satisfied by a pressure contact switch serving to monitor the pressure of a tire.

A first condition that should be satisfied is to effect a closing of the electrical circuit that is both rapid and irreversible as soon as the release pressure has been reached and as long as an acceptable pressure is not reestablished. Most of the known devices are of progressive, continuous and reversible operation, resulting in the risk of the fonnation of sparks by the approach to each other of contact pieces as a result of accidental slight variations in pressure.

A second condition to be satisfied is to achieve completely automatic action, not requiring any outside intervention to return the pressure contact switch into operating condition after release, other than the reinflation of the tire.

Theengagement pressure must be definitely different from the release pressure and independent of it.

A third condition to be satisfied is to make the device invulnerable to any excess pressure. This condition is not satisfied in apparatus containing bimetallic strips or flexible interrupters which are always liable of suffering permanent deformation.

A fourth condition to be satisfied is the miniaturizing of the device. This miniaturizing is necessary not only in order to take into account the small amount of space available to house a pressure contact switch on an automobile wheel but also for operating reasons. The apparatus must operate both on a stationary vehicle and on a vehicle traveling at high speed, and do so with the same preadjusted release pressure. It is therefore advisable that the pressure contact switch be composed of parts that are at the same time very light, very small and subject to very small displacements, in order to reduce to a minimum friction and the influence of centrifugal force and other forces of inertia.

A fifth condition to be satisfied is simplicity of construction, on the one hand, and of operation, on the other hand. This is important not only for reasons of economy-anything which is unnecessarily complex is unnecessarily costly-but also for reasons of utilization, particularly ease of adjustment of the release pressure and ease of positioning with due consideration of the external forces that are to be neutralized.

SUMMARY OF THE INVENTION An object of the present invention is to remedy the shortcomings of conventional pressure contact switches and to provide a pressure contact switch that satisfies all of the conditions noted above.

The pressure contact switch in accordance with the invention comprises a piston subjected on one side to the pressure of the fluid to be monitored and on the other side to the pressure of a calibrated opposing spring. The switch is characterized in that it further comprises, connected to the piston, a coaxial rod shaped in such a manner as to form, on the one hand, a cam means to push a contacting slide capable of sliding in a first bore and, on the other hand, a guide and a stop for a locking slide capable of sliding in a second bore the axis of which is perpendicular to that of the first bore, the two slides being pushed permanently by springs in the direction towards the intersection of the axes of the two bores.

The operation of the device is very simple. When the force exerted on the piston by the fluid exceeds that exerted by the opposing calibrated spring, the piston moves and, driving along the profiled rod, permits the latter, by means of the inclined cocking surface or cam, to push back the contacting slide, which permits the locking slide to extend into the space common to the two perpendicular bores and to block the contacting slide. When the pressure of the fluid drops so that the forces exerted on the piston by the fluid becomes less than that exerted on the piston by the calibrated spring, a movement in the opposite direction of the piston and of the profiled rod commences. The locking slide is carried along and as soon as it emerges from the space common to the two bores, causes a sudden unblocking of the contact slide and the sudden closing of the electrical circuit.

The device in question can easily be miniaturized, the different parts having dimensions of the order of a centimeter or millimeter and the displacements of parts being of the order of a millimeter or even of a tenth of a millimeter.

BRIEF DESCRIPTION OF THE DRAWING An understanding of other aspects of the invention can be gained from a consideration of the following detailed description of a representative embodiment thereof, in conjunction with the appended figures of the drawing, wherein:

FIGS. 1 and 2 are sections through a pressure contact switch in accordance with the invention along a plane contain ing the two axes X-X and Y-Y' of the two bores, FIG. 1 showing the apparatus in the open position of the circuit and FIG. 2 in closed position.

DESCRIPTION OF THE PREFERRED EMBODIMENT The figures show a pressure contact switch I screwed by means of a thread 2 on a connection 3 the end of which intended to be connected to a source of inflation fluid (not shown) is closed by a cap 4. At the opposite end this connection has a nut 5 by means of which the pressure contact switch is connected to the valve of the tire (not shown).

The pressure contact switch has a housing 10 of electrically nonconductive material that has the general shape of a body of revolution around the axis X-X' having a cylindrical lateral appendage of axis Y-Y'. Bore holes of different diameters are formed about axes X-X' and YY'.

In the housing there is a piston 11 which slides in the bore 12. A diaphragm 13 is hermetically fastened on the piston by a crimped washer 14. This diaphragm, whose periphery is compressed between a washer l5 and a shoulder 16 of the connection 3, assures tightness and makes it possible to transmit to the piston 11 the force due to the pressure prevailing in the connection 3. The piston 11 is subjected to the opposing action of a calibrated spring 36 housed in the bore 17 and resting against a shoulder 18 of the housing and the groove 19 of the piston.

On the piston 11 there is screwed a rod 20 which comprises, in succession, a threaded end 21 for membly to the piston 11, a cylindrical portion 22, a shoulder or abutment means 23, a cylindrical-conical inclined cam surface 24 and finally, at its end, a slot 25 to permit screwing by means of a screwdriver. This screwing makes it possible to adjust the pressure at which the pressure contact switch operates. The rod 20 bears on the housing via the bore 26 which is closed by a protective cap 27.

On the rod 20 there slides a locking slide 30 which abuts the shoulder 23 and is held away from the piston 11 by a spring 31 resting against a shoulder 32, on the slide 30 and a shoulder 33 on the piston 11. The diameter of this slide is less than the diameter of the bore 34 provided in the housing 10.

The housing 10 also contains a metal contacting slide 40 housed in a bore 41 of axis- Y-Y' perpendicular to the axis X-X. The contacting slide 40 has a protruding point 44 formed, for instance, of an embedded ball capable of bearing against a portion of the cylindrical-conical inclined cam surface 24. The slide is hollowed in the form of a cup and has a collar 42 capable of coming into contact with a metal washer 45. The slide 40 is pushed in the direction of the rod 20 by a spring 46. The bore 47 which forms an extension of the bore 41 is closed by a metal cap 50 connected by a thread 51 to the housing 10. This cap 50 is of cup shape and comes into contact with the metal washer 45. It furthermore bears a double thimble 52 fastened on the cap via a clamping washer 53 by a bolt 54 and a nut 55, all of metal. An insulating liner 56 insulates the bolt 54 from the cap 50. The metal spring 46 rests against the head 59 of the bolt 54.

The thimble 52 has two metal faces 66 and 67 on either side of an insulating layer 68. Each metal face of the thimble 52 is connected by a conductive wire (not shown) to an input terminal of an electrical assembly (also not shown) intended to transmit or process the signal given by the pressure contact. In this way, the driver of an automotive vehicle can be alerted to the fact of low air pressure in a tire of the vehicle.

As can be seen from FIG. 1, under the action of a pressure in the connection 3 which is higher than that of the calibrated spring 36, the piston 11 has been displaced upward, which has permitted the rod 20, via the inclined cam surface 24, to push back the contact slide 40 to its standby position. The locking slide 30 furthermore maintains the contact slide 40 spaced from the contact washer 45 which is insulated from ground. As shown in FIG. 2, the pressure in the connection 3 having dropped, the piston 11 has moved downward, and at the time when the locking slide 30 has moved to its retracted position in which it has emerged from the contour of the bore 41, the contact slide 40 has suddenly moved to its alarm position in contact with the washer 45, grounding the latter. By screwing the rod 20 to a greater or lesser extent on the piston 11, one can regulate the release pressure, that is to say, the pressure at which the locking slide 30 moves away to permit passage of the contactor 40. The stroke of the rod 20 may be limited to l or 2 mm., thus considerably reducing the friction to be overcome, Furthennore, the different parts of this pressure contact switch can be very small, the housing 10 not exceeding 1 to 2 cm. in its largest dimension.

Experience shows that the release pressure can be defined with great precision (defined within 0.05 bar) and remains constant for a very wide range of speed of the vehicle, even when the pressure contact switch is fastened to the valve of the tire, that is to say, near the rim, where centrifugal forces are greatest.

In one embodiment of the invention there are provided in the connection 3 on opposite sides of the orifice 70 (FIG. 1) two diaphragm valves 71A and 718. Each of these diaphragm valves comprises a moving part 72 which, depending on its position with respect to its support 73, partially closes or completely frees the passage for the air. The two valves 71A and 71B are arranged in opposition so that whatever the direction of flow of the air, one of them is full open, while the other forms a restricted air passage.

The valve 71A located between the orifice 70 and the nut for attachment to the valve of the tire has the function during the inflation of the tire of slowing down the entrance of air. This makes it possible to increase the action of the air on the membrane 13 and tofacilitate the movement of the inclined cocking surface 24. The result is that one can cock the pressure contact switch by using a source of air of lower pressure.

The flap 718 located between the orifice 70 and the valve cap 4 has the function of slowing down the emergence of air when the apparatus is connected to a pressure gauge in order to measure the inflation pressure. One thus avoids creating a vacuum which might, by acting on the membrane 13, release the pressure contact switch.

Thus there is provided in accordance with the invention a new and improved pressure contact switch that is very reliable yet inexpensive. Many modifications of the representative embodiment described herein will readily occur to those skilled in the art, and the invention is to be construed as including all of the embodiments thereof within the scope of the appended claims.

I claim: 1. A pressure contact switch for monitoring the pressure of a fluid, comprising a movable piston, means transmitting to the piston a force due to a pressure of a fluid to be monitored, an opposing calibrated spring bearing on the piston and urging the piston in a direction opposite to the direction in which the piston is urged by the monitored fluid under pressure, rod means connected to the piston and movable therewith, the rod means being formed with a cam surface and abutment means, a contact slide movable between an alarm position and a standby position, biasing means urging the contact slide towards the alarm position locking slide means moving between a locking position wherein it holds the contact slide in the standby position and a retracted position wherein it permits the contact slide to drop into the alann position, and biasing means urging the locking slide means towards the locking position, the abutment means being engageable with the locking slide means, whereby the cam surface moves the contact slide away from the alarm position and the locking slide means holds the contact slide in the standby position so long as the pressure of the fluid acting on the piston is above a predetermined value, and the abutment means forces the locking slide means away from the locking position when the pressure of the fluid acting on the piston drops below a predetermined value, so that the contact slide drops into the alarm position.

2. A pressure contact switch according to claim I further comprising a housing formed with two bores having mutually perpendicular axes, the contact slide being movable in one of the bores and the locking slide means being movable in the other, and the biasing means for the contact slide and the biasing means for the locking slide means respectively urging the contact slide and the locking slide means towards the intersection of the two bores.

3. A pressure contact switch according to claim 1 further comprising at least one valve means limiting the rate of flow of fluid acting on the piston. 

1. A pressure contact switch for monitoring the pressure of a fluid, comprising a movable piston, means transmitting to the piston a force due to a pressure of a fluid to be monitored, an opposing calibrated spring bearing on the piston and urging the piston in a direction opposite to the direction in which the piston is urged by the monitored fluid under pressure, rod means connected to the piston and movable therewith, the rod means being formed with a cam surface and abutment means, a contact slide movable between an alarm position and a standby position, biasing means urging the contact slide towards the alarm position locking slide means moving between a locking position wherein it holds the contact slide in the standby position and a retracted position wherein it permits the contact slide to drop into the alarm position, and biasing means urging the locking slide means towards the locking position, the abutment means being engageable with the locking slide means, whereby the cam surface moves the contact slide away from the alarm position and the locking slide means holds the contact slide in the standby position so long as the pressure of the fluid acting on the piston is above a predetermined value, and the abutment means forces the locking slide means away from the locking position when the pressure of the fluid acting on the piston drops below a predetermined value, so that the contact slide drops into the alarm position.
 2. A pressure contact switch according to claim 1 further comprising a housing formed with two bores having mutually perpendicular axes, the contact slide being movable in one of the bores and the locking slide means being movable in the other, and the biasing means for the contact slide and the biasing means for the locking slide means respectively urging the contact slide and the locking slide means towards the intersection of the two bores.
 3. A pressure contact switch according to claim 1 further comprising at least one valve means limiting the rate of flow of fluid acting on the piston. 